Two-lamp mercury ballast



Nov. 22, 1966 A. R. COLLUCCI 3,287,601

TWO LAMP MERCURY BALLAST Filed Dec. 18, 1963 ANTHONY R. COLLUCCI INVENTOR.

BYM M ATTORNEY United States Patent M TWO-LAMP MERCURY BALLAST Anthony R. Collucci, Ipswich, Mass., assignor to Sylvania Electric Products Inc., acorporation of Delaware Filed Dec. 18, 1963, Ser. No. 331,480 2 Claims. (CL. 315-187) This invention relates to apparatus for starting and operating electric discharge lamps, particularly those of high pressure mercury vapor types. Such apparatus is generally called a ballast.

Prior ballasts have either placed the two lamps in series, in which case the failure of one lamp would put both lamps out, or in parallel, with a separate condenser in series with each lamp, in which case interaction could occur due to insuflicient isolation of the lamp circuits, causing unstable operation. The instability is especially deleterious in socalled hot restarting, that is, in attempting to restart shortly after the lamps have stopped operating due to a temporary voltage interruption in the line or for some other reason. The parallel type circuit will usually cause the lamps to alternately go on and off in a so-called flipflop manner when re-starting is attempted while the lamps are still hot, at high mercury pressure from the heat of a recently interrupted operation of the lamp. The electrodes are damaged by this sort of operation.

The present invention eliminates such disadvantages by operating each lamp from a separate Winding 01f a single transformer, thus providing two isolated circuits for operation of the lamps. To facilitate starting, however, one end of one winding can be connected to one end of the other winding to place them in series-aiding relationship, which means that there is a series circuit including the two transformer coils, a series condenser, one lamp, another lamp, and another series condenser for the latter lamp. There is then a connection between the two ends of the lamps which are connected together and the two ends of the windings which are connected together, forming a kind of bridge circuit.

Since both windings can be on the same leg of the transformer, with leakage reactanoe between these two windings and the primary winding, the starting of one lamp will transiently increase the voltage available across the other lamp, thereby starting it also.

For sequential operation, the lamp which is to start first should have more turns in its winding, or more voltage induced in the winding, so that it will definitely start with out any assistance from the other lamp. The first lamp will then start whether or not the second lamp starts.

However, if the first lamp does not start, the other lamp may not start, unless the circuit is used with a capacitor connected across at least parts of the two secondary windings in series in order to raise the starting voltage, or unless the number of turns on the secondary winding for the second lamp, with the added flux in the core from the current through the other lamp, is sufiicient to start the lamp. After the starting of the first lamp, the increased flux in the core from the current flow to that lamp, will increase the secondary voltage to the other lamp about We have discovered, however, that the best operation occurs when both secondaries have about the same number of turns, and the open circuit voltage of each is suflicient to start the lamp. Because the starting of one lamp 3,287,601 Patented Nov. 22, 1966 increases the starting voltage to the other, and because of the electrical isolation of the two lamps in other respects, the h-ot-restriking problem is solved by my invention. The two secondaries can be completely separate, if desired, and can be used without a common center connection.

Other features objects and advantages ofthe invention will be apparent from the following specification, taken in connection with the accompanying figure in which:

'In the figure, a closed magnetic core 1 preferably of a good grade of transformer iron such as silicon steel, has [four legs 2, 3, 4, 5, cforming a closed magnetic circuit with the leg 6 between legs 3 and 5 in order to provide a shunt path for magnetic leakage between the primary windings 7, 8 and the secondary windings 9, 10. The windings 7 and 8, can be connected either in series or in parallel. In practice they are generally made so that they can be connected in parallel for volt operation or in series for 220 volt operation.

The secondary coils 9 and 10 are connected in seriesaiding relationship, and between the outer ends 11 and 12 the capacitor 13, lamp 14, lamp 15 and capacitor 16 are connected in series. A connection 17 extends from the connection 18 between the lamps 14 and 15 and connection 19 between the two coils 11 and 12. Bleeder resistances 20 and 21, respectively, are connected across each condenser 13 and 16 in order to discharge the capacitors When the circuit is open, as is customary in the use of capacitors.

An additional capacitor 22 may be connected across part or all of the windings 9 and 10, as shown, in order to increase the voltage available for starting the lamps. This condenser can be omitted if desired, in which case a few more turns may have to be added to the windings 9 and 10 to increase the voltage.

A voltage of about 260 volts is generally desirable for starting the usual types Olf 400 Watt high pressure mercury lamps. The open circuit voltage of winding 9 is about 260 volts in the example described, that across winding 10 about 200 volts, with condenser 22 out of circuit. The capacitors 13 can be of about 26 microfarads and capacitor 22 if used, can be of 2.3 microfarads. The resistors 20 and 21 can be of 1 megohm for example, although the exact value is not critical. In one embodiment the transformer core 1 had outside dimensions of 67 inches by 3%; inches by 3", and inside dimension of 4% inches by 1 inches by 3", with the shunt 6 being about inch by inch by 3% inches. The two coils 7 and 8 had about 142 turns each, and coils 9 and 10 had about 255 turns each. The'lamps 14 and 15 were standard 400 watt high pressure vapor lamps with a starting voltage of about 225 volts and an operating voltage of about volts.

The number of turns on winding 9 can generally be about 20% less than the number on winding 10, if sequential starting is desired.

Although a particular embodiment of the invention has been described many modifications may be made therein without departing from the scope of the invention set forth in the accompanying claims.

What I claim is:

1. A circuit for starting and operating electric discharge lamps comprising a transformer having at least one primary winding and at least two secondary windings, each of said secondary windings having a capacitor and an electric discharge lamp connected in series with it, the two secondaries being both on the same leg of the transformer so that current flow through one secondary will increase the flux through the other, and a third capacitor, said third capacitor being connected across at least part of said two secondary windings to raise the starting voltage.

2. A circuit for starting and operating electric discharge lamps comprising a transformer having at least one primary winding and at least two secondary windings, each of said secondary windings having a capacitor and an electric discharge lamp connected in series with it, the two secondaries being both on the same leg of the transformer so that current flow through one secondary will increase the flux through the other, the primary being on References Cited by the Examiner UNITED STATES PATENTS 4/1934 Comstock 315-257 7/1936 Wirz 336-460 FOREIGN PATENTS 1,193,834 11/1959 France.

JAMES WJLAWRENCE, Primary Examiner.

C. R. CAMPBELL, Assistant Examiner. 

1. A CIRCUIT FOR STARTING AND OPERATING ELECTRIC DISCHARGE LAMPS COMPRISING A TRANSFORMER HAVING AT LEAST ONE PRIMARY WINDING AND AT LEAST TWO SECONDARY WINDINGS, EACH OF SAID SECONDARY WINDINGS HAVING A CAPACITOR AND AN ELECTRIC DISCHARGE LAMP CONNECTED IN SERIES WITH IT, THE TWO SECONDARIES BEING BOTH ON THE SAME LEG OF THE TRANSFORMER SO THAT CURRENT FLOW THROUGH ONE SECONDARY WILL INCREASE THE FLUX THROUGH THE OTHER, AND A THIRD CAPACITOR, SAID THIRD CAPACITOR BEING CONNECTED ACROSS AT LEAST PART OF SAID TWO SECONDARY WINDINGS TO RAISE THE STARTING VOLTAGE. 